A data recording disk drive has a plurality of capacitive sensors, each sensor facing a surface of an associated disk, a capacitance sensing circuit for converting the sensed capacitance to a voltage representative of the distance between the sensor and the disk surface, and a feedforward controller that receives the voltage signal. The feedforward controller has a transfer function with gain and phase characteristics designed to match the transfer function from the out-of-plane disk vibration to the position of the read/write head while accounting for the effects of the sensor dynamics and the dynamics of the actuator. The output from the feedforward controller is combined with the output from the disk drive's servo feedback controller so that the effects of disk vibration on track misregistration of the head are removed from the control signal to the actuator.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A disk drive having a rotatable magnetic recording disk with a plurality of data tracks and a recording head movable across the disk surface for reading and/or writing data in the tracks, and wherein the tracks contain head position information detectable by the head and the head experiences a track misregistration (TMR) frequency response as a result of out-of-plane vibration of the rotating disk, the disk drive comprising: an actuator for moving the head across the disk surface; a head position feedback controller responsive to position information detected by the head for generating a head position control signal; a capacitive sensor facing the disk surface; a capacitance sensing circuit coupled to the sensor for generating a signal representative of the distance between the sensor and the disk surface; and a feedforward controller responsive to the distance signal for generating a correction signal, the correction signal being combined with the head position control signal to generate an actuator control signal, the feedforward controller having gain and phase characteristics to substantially match the frequency response from the out-of-plane vibration to the TMR while accounting for the effects of the dynamics of the capacitive sensor and actuator.
2. The disk drive of claim 1 wherein the feedforward controller gain is variable, the gain value being selected in response to radial position of the head on the disk surface.
3. The disk drive of claim 2 wherein the disk drive includes a head movable across the disk surface opposite the disk surface faced by the capacitive sensor, and wherein the polarity of the selected gain value is switchable in response to the head selected for reading or writing.
4. The disk drive of claim 1 wherein the feedforward controller phase is variable, the phase value being selected in response to radial position of the head on the disk surface.
5. A disk drive having a rotatable magnetic recording disk with a plurality of data tracks and a recording head movable across the disk surface for reading and/or writing data in the tracks, and wherein the tracks contain head position information detectable by the head, the disk drive comprising: an actuator for moving the head across the disk surface; a head position feedback controller responsive to position information detected by the head for generating a head position control signal; a capacitive sensor facing the disk surface; a capacitance sensing circuit coupled to the sensor for generating a signal representative of the distance between the sensor and the disk surface; and a feedforward controller responsive to the distance signal for generating a correction signal, the correction signal being combined with the head position control signal to generate an actuator control signal; wherein the distance between the sensor and the disk surface includes a component that is substantially repeatable for each angular location on the disk surface, and wherein the feedforward controller is responsive to the distance signal after removal of said component.
6. The disk drive of claim 5 further comprising a digital servo processor comprising the feedback controller and the feedforward controller, the processor combining the head position control signal and the correction signal and generating a digital actuator control signal.
7. The disk drive of claim 6 further comprising an analog-to-digital converter between the capacitance sensing circuit and the processor for converting the distance signal to a digital distance signal usable by the processor.
8. The disk drive of claim 7 wherein the processor subtracts said component from the digital distance signal.
9. The disk drive of claim 6 wherein the actuator is a voice coil motor (VCM) and further comprising a digital-to-analog converter for converting the digital actuator control signal to an analog actuator control signal to the VCM.
10. A magnetic recording disk drive comprising: a housing; a spindle motor attached to the housing; a magnetic recording disk having a plurality of generally concentric data tracks containing head position servo information, the disk being mounted to and rotatable by the spindle motor about an axis of rotation, the disk experiencing axial vibration during its rotation; a recording head for reading and writing data in the tracks, the head experiencing a trackmisregistration (TMR) frequency response as a result of axial vibration of the rotating disk; a voice coil motor (VCM) actuator for moving the head generally radially across the tracks and for maintaining the head on a desired track during reading and writing; servo electronics for converting servo information detected by the head to a digital position error signal (PES); a capacitive sensor attached to the housing and facing the disk surface; a capacitance sensing circuit coupled to the sensor for generating an analog signal representative of the distance between the sensor and the disk surface during axial vibration of the disk; an analog-to-digital converter for converting the analog distance signal to a digital distance value; a digital servo processor comprising a feedback controller for generating a head position control value from the PES and a feedforward controller having gain and phase characteristics to substantially match the TMR frequency response for generating a correction to the head position control value from the digital distance value, the processor outputting a corrected head position control value; and a digital-to-analog converter for converting the corrected head position control value to an analog actuator control signal to the VCM.
11. The disk drive of claim 10 wherein the feedforward controller gain is variable, the feedforward controller generating a correction to the head position control value using a gain value selected in response to radial position of the head on the disk surface.
12. The disk drive of claim 11 wherein the processor includes memory for storing digital values, and further comprising a table of head radial position values and associated gain values stored in the memory.
13. The disk drive of claim 10 wherein the feedforward controller phase is variable, the feedforward controller generating a correction to the head position control value using a phase value selected in response to radial position of the head on the disk surface.
14. The disk drive of claim 13 wherein the processor includes memory for storing digital values, and further comprising a table of head radial position values and associated phase values stored in the memory.
15. The disk drive of claim 10 wherein the processor includes memory for storing digital values, wherein the distance between the sensor and the disk surface includes a component that is substantially repeatable for each angular location on the disk surface, and further comprising a table of disk angular locations and associated distance component values stored in the memory, the processor modifying the digital distance value with a component value from the table prior to generation of the correction to the head position control value by the feedforward controller.
16. The disk drive of claim 10 further comprising a plurality of disks stacked on the spindle motor and a plurality of capacitive sensors, each sensor being associated with and facing a surface of an associated disk.
17. The disk drive of claim 16 wherein the capacitance sensing circuit includes a multiplexer for selecting one of said capacitive sensors.
18. The disk drive of claim 16 wherein the plurality of capacitive sensors comprises a sensor for each disk surface.
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September 30, 2004
March 14, 2006
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